Abstract Details

Purpose:

The macula is an attractive target for first in man cell replacement therapies, particularly in the context of age-related macular degeneration (AMD). However, the role of immunosuppressive regimens as well as surgical protocols on submacular RPE graft integration remain less understood. Here we present a novel monkey model platform for retinal pigment epithelium (RPE) replacement with monolayer grafts with a disrupted immune privilege under the macula.

Setting:

The primary outcome measure was to assess submacular integration of hESC-RPE xenografts in a primate model with disrupted blood retinal barrier, secondary outcomes were surgical macular dynamics assessed by iOCT and safety.

Methods:

Human embryonic stem cell derived RPE (hESC-RPE) were grown with an optimized protocol on translucent biostable cell carriers. When mature, they were shipped alive from Finland to Singapore. Macaques were immunosuppressed prior to surgery and throughout 4 week postoperative follow up with either systemic (n=10) or intravitreal sirolimus (n=4). All animals received systemic minocycline and doxycycline. Fourteen eyes of monkeys (n= 14) underwent vitrectomy with removal of posterior cortical vitreous. Several modes to create a bleb retinal detachment (bRD) with subretinal BSS injection throughout the posterior pole were explored. The RPE xenotransplant was delivered through a retinotomy onto a RPE wound underneath the macula using custom instrumentation. A fluid air exchange flattened the bRD. All key surgical steps were guided with intraoperative OCT (iOCT). The animals were followed up with a combined SLO/ OCT device at 3, 7, 14 and 28 days postoperatively. Pattern and full-field ERG were performed at baseline, then at 7, 14 and 28 days postOP. Animals were then processed for H&E histology.

Results:

Mature hESC-RPE monolayers suitable for transplantation were derived within 4-6 weeks. Live shipment did not alter morphology or transepithelial electrical resistance of the cultures. The submacular implantation was successful in 12 of 14 animals, one animal served as sham control and 1 developed an iatrogenic cataract. The fluid wave following subretinal BSS resulted into either full thickness foveal tear (n=10), BSS-induced cystoid macular edema with or without foveal de-roofing (n=3), or complete foveal detachment (n=1). A combination of starting the fluid wave from 2DD inferonasal to the fovea under PFC resulted in the most controllable detachment of neurosensory retina. iOCT controlled visualization of subretinal fluid drainage after fluid air exchange greatly facilitated complete retinal reattachment. In preliminary data, foveal atrophy on SD-OCT was observed at postOP day 28 in 3/8 eyes evaluated and seemed correlated to the degree of surgical trauma. Full field ERG recorded at day 28 postOP was indistinguishable from baseline. Preliminary pattern ERGs showed amplitude recovery compared to baseline values in 5 of 8 animals at 28 days postOP. Preliminary histology showed intact photoreceptors above the xenoRPE monolayer.